UNIVERSITY  OF  CALIFORNIA  PUBLICATIONS 

COLLEGE  OF  AGRICULTURE 
AGRICULTURAL  EXPERIMENT  STATION 

BERKELEY,  CALIFORNIA 


Melaxuma    of  the  Walnut,  "Juglans    regia 

(A  PRELIMINARY  REPORT) 


By  HOWARD  S.  FAWCETT 


BULLETIN   No.   261 

Berkeley,  Cal.,  November,  1915 


California 

State  Printing  Office 

1915 

19511 


Benjamin  Ide  Wheeler,  President  of  the  University. 

EXPERIMENT    STATION    STAFF 

HEADS   OF   DIVISIONS 

Thomas  Forsyth  Hunt,  Director. 

Eugene  W.  Hilgard,  Agricultural  Chemistry   (Emeritus). 

Edward  J.  Wickson,  Horticulture  (Emeritus). 

Herbert  J.  Webber,  Director  Citrus  Experiment  Station  ;  Plant  Breeding. 

Hubert  E.  Van  Norman,  Vice-Director ;  Dairy  Management. 

William  A.  Setchell,  Botany. 

Myer  E.  Jaffa,  Nutrition. 

Robert  H.  Loughridge,  Soil  Chemistry  and  Physics   (Emeritus). 

Charles  W.  Woodwortii,  Entomology. 

Ralph  E.  Smith,  Plant  Pathology. 

J.  Eliot  Coit,  Citriculture. 

John  W.  Gilmore,  Agronomy. 

Charles  F.  Shaw,  Soil  Technology. 

John  W.  Gregg,  Landscape  Gardening  and  Floriculture. 

Frederic  T.  Bioletti,  Viticulture  and  Enology. 

Warren  T.  Clarke,  Agricultural  Extension. 

John  S.  Burd,  Agricultural  Chemistry. 

Charles  B.  Lipman,  Soil  Chemistry  and  Bacteriology. 

Clarence  M.  Haring,  Veterinary  Science  and  Bacteriology. 

Ernest  B.  Babcock,  Genetics. 

Gordon  H.  True,  Animal  Husbandry. 

James  T.  Barrett,  Plant  Pathology. 

Fritz  W.  Woll,  Animal  Nutrition. 

A.  V.  Stubenrauch,  Pomology. 

Walter  Mulford,  Forestry. 

W.  P.  Kelley,  Agricultural  Chemistry. 

H.  J.  Quayle,  Entomology. 

Elwood  Mead,  Rural  Institutions. 

J.  B.  Davidson,  Agricultural  Engineering. 

H.  S.  Reed,  Plant  Physiology. 

William  G.  Hummell,  Agricultural  Education. 

Leon  M.  Davis,  Dairy  Industry. 

John  E.  Dougherty,  Poultry  Husbandry. 

Frank  Adams,  Irrigation  Practice. 

David  N.  Morgan,  Assistant  to  the  Director. 

Mrs.  D.  L.  Bunnell,  Librarian. 

division  of  soil  chemistry  and  bacteriology 
C.  B.  Lipman  W.  F.  Gericke 

L.  T.  Sharp  M.  A.  Klein 

L.  E.  Bailey 


CONTENTS. 


Page 

Introduction 133 

Description  of  the  Disease 133 

Investigation  as  to  Cause  op  Melaxuma 134 

Previous  Work   : 134 

Inoculations  with  Diseased  Tissue 134 

Inoculations  with  Cultures  of  Dothiorella 136 

Reisolation  of  the  Fungus 137 

Willows  Affected  with  Melaxuma 137 

Tabulated  Results  of  Inoculations  on  Walnut  and  Willow  Trees 138 

The   Fungus   140 

Probable  Methods   op  Natural   Infection 140 

Experiment  for  Control 143 

Treatment   Suggested   145 

Summary    148 


2—19511 


Digitized  by  the  Internet  Archive 

in  2012  with  funding  from 

University  of  California,  Davis  Libraries 


http://www.archive.org/details/melaxumaofwalnut261fawc 


MELAXUMA  OF  THE  WALNUT,  JUGLANS  REGIA.* 

(PRELIMINARY  REPORT.) 

Howard  S.  Fawcett. 

INTRODUCTION. 

It  is  the  purpose  of  this  bulletin  to  report  the  results  of  an  investiga- 
tion begun  in  June,  1913,  relating  to  the  cause  and  control  of  a 
comparatively  new  disease  of  English  walnut  trees  in  California.  This 
disease,  known  as  Melaxuma,  which  occurs  in  the  form  of  black  cankers 
in  the  crotches  and  limbs,  and  occasionally  in  the  form  of  a  sudden 
wilting  and  dying  of  the  branches,  has  been  noticed  by  walnut  growers 
in  Santa  Barbara  County  for  a  number  of  years  (at  least  since  1909), 
but  has  only  attracted  serious  attention  during  the  past  two  or  three 
years. 

Because  of  the  oozing  of  dark  watery  material  to  the  surface  of 
affected  areas,  this  disease  is  often  confused,  under  the  name  of  "  black 
sap,"  with  sunburn,  frost  injury,  injuries  to  the  bark  in  cultivation, 
injury  from  the  decay  of  wood  at  places  where  limbs  have  been  cut 
off,  and  other  troubles  in  which  a  "black  sap"  may  ooze  out  during 
the  active  growing  period  of  the  tree.  It  should  not  be  taken  for 
granted,  therefore,  that  because  a  black  ooze  is  seen  on  the  trunk  or 
larger  limbs  of  a  walnut  tree  that  Melaxuma  is  necessarily  present. 

As  the  term  "black  sap"  has  already  been  used  by  R.  E.  Smith t 
to  designate  a  result  of  sunburning,  this  name  was  not  considered 
suitable  for  the  disease  here  being  considered.  The  word  Melaxuma, 
derived  from  two  Greek  words  meaning  "black"  and  "juice,"  was 
therefore  adopted  and  is  now  in  fairly  common  use  to  designate  the 
disease  herein  described. 

DESCRIPTION  OF  THE  DISEASE. 

Melaxuma  shows  its  effect  most  strikingly  during  the  summer  after 
the  growth  is  well  started.  On  trees  severely  affected  at  that  time, 
there  will  be  seen  large  black  sunken  cankers  on  the  trunk  and  larger 
limbs  and  often  a  sudden  wilting  of  smaller  limbs  and  twigs.  This 
sudden  wilting  of  the  smaller  limbs  is  so  different  from  the  effects  of 
walnut  blight  or  bacteriosis,  that  it  is  easily  distinguished  from  that 
disease. 

The  most  common  location  for  Melaxuma  cankers  is  at  the  crotch  of 
the  tree  where  the  first  limbs  join  the  trunk.  (Fig.  1.)  The  first 
evidence  of  the  disease  is  often  a  black  area  on  the  otherwise  greyish 
bark  which  looks  like  a  dab  of  tar.     (Fig.  2.)     This  is  due  to  the 


*Paper   No.    18,    Citrus   Experiment    Station,    College   of   Agriculture,    University    of 
California,   Riverside,   California. 

f'Walnut  Culture  in  California,"  Bulletin  231,  page  373. 


134  UNIVERSITY   OP    CALIFORNIA EXPERIMENT    STATION. 

staining  of  the  bark  by  a  black  watery  substance  that  forms  under  it. 
The  diseased  area  later  becomes  slightly  sunken,  shrinks  and  cracks. 
The  " black  sap"  then  oozes  out  in  considerable  quantities  and  stains 
the  bark  as  it  runs  down  the  limb  or  trunk.  The  wood  underneath  is 
discolored  for  a  short  distance  and  this  discoloration  usually  extends 
beyond  the  margin  of  the  killed  bark.  The  diseased  areas,  as  a  rule, 
do  not  extend  entirely  around  a  limb  in  one  season,  but  affect  only 
about  one-third  or  one-half  the  circumference  of  the  bark.  (Fig.  3.) 
Later  in  the  summer  or  fall  the  increase  in  the  size  of  the  areas  is 
slower  and  often  appears  to  be  stopped.  Part  of  the  margin  of  the 
canker  may  dry  out  and  begin  to  heal  over,  while  the  other  continues 
to  advance  or  remains  stationary  until  the  next  spring  when  it  begins 
to  advance  rapidly  again.  A  few  cankers  on  large  limbs  of  vigorous 
trees  may  even  heal  over  without  treatment,  but  this  rarely  takes 
place.  More  often  there  is  an  enlargement  from  year  to  year  which 
in  two  or  more  years  extends  entirely  around  a  large  limb,  causing  it 
to  wilt  and  die.  (Fig.  1,  A  and  B.)  These  limbs  occasionally  wilt 
suddenly,  the  dried-up  nuts  and  leaves  remaining  attached  for  some 
time.  When  cankers  occur  on  the  trunks  they  generally  follow  some 
injury  to  the  bark  made  by  a  plow,  cultivator  or  other  instruments 
used  in  the  cultivation  of  the  orchard. 

Further  out  on  the  larger  branches  diseased  cankers  usually  start 
either  at  the  forks  of  branches  or  at  the  base  of  a  small  twig  which  has 
first  been  killed  back  to  the  larger  branch.  In  trees  severely  attacked, 
the  bark  and  wood  on  branches  one-fourth  to  one-half  inch  in  diameter 
may  be  killed  rapidly  and  the  entire  branch  beyond  the  affected  place 
suddenly  withered.  The  dried  leaves  and  half-formed  nuts  often 
remain  attached  to  the  branch.  In  many  cases,  the  smaller  branches 
are  not  so  commonly  affected  as  the  larger  ones. 

INVESTIGATION  AS  TO  THE  CAUSE  OF  MELAXUMA. 
Previous   work. 

The  first  investigation  of  the  disease  was  begun  in  the  early  part 
of  1913,  by  W.  H.  Nixon  and  C.  A.  Hollister,  students  of  the  University 
of  California,  who  proved  that  the  disease  was  infectious  by  transmit- 
ting it  from  diseased  cankers  to  perfectly  healthy  limbs  by  means  of 
cuts  with  an  infected  ax  or  chisel,  and  also  by  inserting  pieces  of 
diseased  bark  from  active  cankers  into  healthy  limbs.  Mr.  Hollister 
had  noticed  that  in  an  orchard  pruned  with  an  ax,  a  year  or  so  before, 
the  disease  had  apparently  been  spread  from  a  few  diseased  trees 
over  a  greater  part  of  the  orchard. 

Inoculations  with  diseased  tissue. 

In  June,  1913,  while  the  writer  was  with  the  California  State  Com- 
mission  of  Horticulture,   a   further  investigation  of  the   disease  was 


[Bulletin  261] 


MELAXUMA   OF    THE    WALNUT. 


135 


Fig.  1.  Melaxuma  on  walnut  trees.  (A)  Showing  limbs  killed  by  the  dis- 
ease. (B)  Showing  old  cankers  from  which  the  bark  has  fallen  away. 
(C)  Showing  a  number  of  cankers  from  which  "black  sap"  is  oozing.  The 
arrows  denote  the  location  of  cankers. 


136  UNIVERSITY   OF    CALIFORNIA EXPERIMENT    STATION. 

taken  up,  not  only  at  the  request  of  Mr.  C.  W.  Beers,  Horticultural 
Commissioner  of  Santa  Barbara  County,  but  also  at  the  request  of 
Messrs.  Nixon  and  Hollister,  who  did  not  wish  to  continue  further 
with  the  work.  The  experiments  that  Nixon  and  Hollister  had  started 
were  examined.  About  twenty  inoculations  had  been  made  into  healthy 
limbs;  seven  with  diseased  bark,  five  with  knives  or  chisels  that  had 
first  been  infected  by  cutting  into  active  cankers,  and  eight  with  an 
ax  infected  in  the  same  way.  Six  cuts  with  sterilized  instruments 
had  also  been  made  as  checks.  The  bark  of  the  limbs  had  been  dis- 
infected with  corrosive  sublimate,  1-1000,  previous  to  inoculation  and 
afterwards  wrapped  with  paraffined  paper.  In  from  one  to  two  months 
nearly  all  the  inoculations  were  showing  infection  and  later  developed 
typical  Melaxuma  cankers.  One  of  the  check  cuts  had  become  acci- 
dently  infected.     The  others  were  healing  normally. 

Late  in  June,  1913,  further  inoculation  experiments  by  the  writer 
with  material  not  only  from  the  diseased  cankers,  but  from  the  smaller 
withered  limbs,  showed  the  same  results  as  those  obtained  by  Nixon 
and  Hollister.  In  these  inoculation  experiments,  diseased  bark  and 
wood  was  taken  from  active  cankers  on  large  limbs  and  put  into  both 
large  and  small  limbs,  and  diseased  bark  was  also  taken  from  small 
withering  limbs  and  put  into  both  large  and  small  limbs,  with  the 
result  that  the  withering  of  the  smaller  limbs  and  the  production  of 
the  characteristic  black  cankers  were  proved  to  be  due  to  the  same 
cause.  At  this  time  a  fungus,  a  species  of  DotMorella,  was  discovered 
in  these  diseased  cankers  and  also  on  the  withered  limbs,  and  pure 
cultures  were  obtained. 

Inoculations  with  cultures  of  Dothiorella. 

In  the  latter  part  of  July,  inoculations  were  made  by  placing  bits  of 
fungus  from  these  pure  cultures  into  cuts  in  healthy  limbs.  It  was 
found  that  when  this  fungus  was  placed  in  small  cuts  in  healthy  large 
limbs,  it  produced  black  cankers,  and  when  placed  in  cuts  in  small 
limbs,  it  killed  the  bark  and  wood  rapidly  and  caused  a  sudden  wilting 
of  the  branch  beyond;  both  effects  being  characteristic  of  the  disease 
as  it  occurs  naturally.  Similar  cuts  made  in  another  part  of  the  same 
tree  in  healthy  limbs  without  the  insertion  of  the  fungus  healed  up 
perfectly  without  producing  any  cankers  or  causing  any  " black  sap" 
to  run  out.  One  of  these  inoculations  will  be  described  (the  results 
of  the  others  are  given  in  Tables  1  and  2)  :  This  inoculation  was  made 
on  a  two  and  one-half  inch  limb  July  31,  1913,  by  inserting  a  bit  of 
fungus  from  a  pure  culture  into  a  small  cut,  and  tying  paraffined  paper 
over  it.  A  similar  cut  was  made  and  wrapped  two  feet  further  out  on 
the  same  limb  without  the  insertion  of  the  fungus. 


[Bulletin  261]  melaxuma  of  the  walnut.  137 

On  September  17,  1913,  an  area  of  bark  2J  inches  long  and  2  inches 
wide,  surrounding  the  inoculated  cut,  was  black  and  a  dark  watery 
liquid  was  oozing  from  it. 

By  April  29,  1914,  the  killed  area,  now  a  typical  Melaxuma  canker, 
had  become  4J  inches  long  and  had  involved  about  two-thirds  of  the 
circumference  of  the  limb.  Abundant  pycnidia  of  Dothiorella  were 
present  over  an  area  2  by  1  inches  and  the  affected  bark  was  sunken 
and  cracked  with  dark  liquid  oozing  out  at  one  edge  where  the  canker 
appeared  to  be  enlarging.  On  the  other  edge  the  progress  of  the 
fungus  had  apparently  been  stopped. 

The  limb  was  cut  off  at  this  time  and  the  greatest  depth  to  which 
the  wood  underneath  was  stained  was  found  to  be  about  one-fourth  of 
an  inch.  The  check  cut  two  feet  further  out  had  healed  perfectly 
without  dying  of  bark  or  oozing  of  "black  sap."  A  considerable 
number  of  similar  inoculations,  giving  similar  results  (see  Tables 
1  and  2),  seemed  to  prove  conclusively  that  this  fungus  was  the  causal 
agent  in  producing  the  disease. 

Reisolation  of  the  fungus. 

Pure  cultures  of  the  fungus,  the  same  that  had  been  used  in  the 
inoculation,  were  isolated  from  bits  of  the  inner  bark  from  the  outer- 
most edge  of  the  affected  area  of  the  inoculation  just  described.  The 
fungus  was  also  reisolated  from  seven  other  artificially  produced 
cankers  of  inoculations  recorded  in  Table  1. 

WILLOWS  AFFECTED  WITH   MELAXUMA. 

In  August,  1914,  cankers  identical  with  those  on  walnut  trees  were 
discovered  in  the  arroyo  willow  (Salix  lasiolepis)  in  Santa  Barbara 
County.  On  microscopic  examination,  the  same  fungus  appeared  to 
be  present  on  the  willows,  and  the  same  fungus  was  isolated  from  them. 
Inoculations  were  then  made  by  inserting  the  fungus  in  cuts  in  the 
healthy  bark  of  both  walnut  and  willow  trees,  with  the  result  that 
typical  Melaxuma  cankers  were  produced  on  both  the  walnut  and  the 
willow.  (Fig.  4.)  Cankers  were  found  on  willow  trees  not  only  on 
the  edge  of  walnut  orchards  but  on  trees  growing  far  removed  from 
walnut  orchards.  It  is  believed  that  the  disease  may  have  originally 
come  from  the  willows  to  the  walnut  trees.  The  transmission  of  the 
disease  in  many  cases  was  probably  hastened  by  the  former  practice 
of  propping  the  lower  limbs  of  walnut  trees  with  poles  cut  from  the 
nearby  willows.  Willows  in  many  sections  of  California  are  commonly 
attacked  by  certain  borers,  but  the  Melaxuma  cankers  are  quite  distinct 
from  the  typical  borer  injury. 


138  UNIVERSITY   OF    CALIFORNIA EXPERIMENT    STATION. 

TABULATED   RESULTS  OF   INOCULATIONS  ON   WALNUT  AND 
WILLOW  TREES. 

The  general  results  of  the  inoculation  experiments  have  already  been 
discussed  under  the  heading  of  "Investigations  as  to  the  Cause." 
These  inoculations  were  made  in  order  to  prove  definitely  whether 
or  not  the  disease  was  infectious,  and  whether  the  Dothiorella  fungus 
found  commonly  associated  with  it,  had  anything  to  do  with  its 
occurrence.  In  all  these  experiments,  except  Nos.  12  and  13,  small 
cuts  were  made  through  the  bark  with  a  sharp  sterile  knife  and  the 
material  for  inoculation  inserted,  after  which  the  cuts  were  covered 
with  paraffined  paper  held  with  raffia.  In  most  cases,  the  bark  at  the 
place  where  the  inoculation  was  to  be  made  was  first  cleansed  by  rubbing 
with  a  cloth  moistened  with  alcohol.  As  will  be  seen  in  the  table,  there 
were  made  with  nearly  every  cut  for  an  inoculation,  a  similar  cut  into 
which  nothing  was  placed,  this  being  a  check  for  the  purpose  of  com- 
parison to  determine  whether  or  not  the  cutting  of  the  bark  alone 
would  cause  the  cankers  to  form.  It  will  be  seen  from  the  results 
that  every  one  of  these  check  cuts  healed.  From  only  one  check  cut 
a  small  amount  of  "black  sap"  oozed  before  healing. 


[Bulletin  261] 


MELAXUMA    OF    THE    WALNUT. 


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3 

o 

P, 

03 

c 

w 

rk  sunken  and  black 
therwise  as  above. 

,_ 

03          O 

rt 

PQ 

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CJ 

-d 

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3 

j2 

hes  wide, 
inches  wi 

CJ 

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Killed  area  6  inches  long, 

flowing.     Fig.  4a. 
Killed  area  3  inches  long  b 
Out  healed  perfectly. 

tH            CM 

CJ             0J 

d             d£ 

-l->            +J     w 

8    86 

140  UNIVERSITY    OF    CALIFORNIA — EXPERIMENT    STATION. 

THE  FUNGUS. 

On  the  surface  of  the  dead  bark  of  the  Melaxuma  cankers,  usually 
sonic  weeks  after  they  first  begin  to  show,  will  be  seen  minute  dark 
pustules  which  have  formed  in  the  bark  and  pushed  up  through 
the  surface.  These  contain  the  pycnidia,  usually  a  number  crowded 
together,  in  which  the  hyaline  spores  are  formed.  The  spores  escape 
in  great  numbers  from  a  small  opening  in  the  top  of  the  pycnidia  and 
are  the  sources  of  infection  from  which  new  cankers  may  be  produced. 

A  microscopic  study  of  the  fungus  when  it  was  first  found  on  the 
cankers  showed  that  it  was  apparently  a  species  of  the  genus  Dothiorella. 
A  study  of  the  literature  has  been  made  and  it  has  been  found  that  at 
least  four  species  of  this  genus  have  been  described  as  occurring  on 
either  walnuts  or  willows.  Specimens  from  the  Melaxuma  cankers 
on  walnut  were  sent  to  Mrs.  Flora  Patterson,  Mycologist,  Bureau  of 
Plant  Industry,  who  kindly  examined  them  and  reported  that  the 
fungus  could  safely  be  assigned  to  Dothiorella  gregaria  Sacc.  In  com- 
paring the  specimens  on  walnut  with  specimens  of  Dothiorella  gregaria, 
Mrs.  Patterson  writes,  "while  the  measurements  of  your  material  and 
those  given  for  Dothiorella  gregaria  are  not  exactly  the  same,  there  is 
no  more  difference  than  has  been  noted  in  sections  made  from  the  latter 
species  as  distributed  in  Cavara-Fungi  Longobordias  exsiccati  No.  138 
on  Populus  nigra."  The  fungus  as  it  occurs  on  walnuts  in  California 
forms  dark  pycnidia,  occurring  either  singly  or  in  groups.  The 
pycnidia  (spore-holding  bodies)  are  flask-shaped,  and  are  180  to  260 
microns*  in  diameter,  with  small  openings  (ostiola)  at  the  outer  ends 
through  which  the  spores  discharge.  The  hyaline,  one-celled,  spindle- 
shaped  spores  are  20  to  26  microns  long,  and  5  to  7  microns  wide,  and 
are  born  on  basidia  about  10  to  15  microns  long  and  3  to  4  microns 
wide.  The  measurements  of  the  spores  given  for  Dothiorella  gregaria 
by  Eabenhorstf  are  18  to  22  microns  long  by  6  to  6.5  wide,  and  the 
fungus  is  reported  to  occur  on  Cornus,  Populus,  Salix,  etc.,  in  Italy 
and  France.  As  far  as  known  the  fungus  has  not  been  reported  to 
cause  any  serious  injury  to  trees  in  Europe. 

PROBABLE  METHODS  OF  NATURAL  INFECTION. 

As  was  stated  before,  the  usual  place  for  cankers  to  begin  is  at  the 
crotches  of  the  large  limbs,  or  at  forks  of  branches,  or  where  a  smaller 
twig  joins  a  main  branch.  They  often  start  also  at  injured  places  at 
any  point  on  the  bark  of  the  trunk  or  branches. 

On  an  examination  of  older  walnut  trees  it  will  be  seen  that  at  the 
crotches  or  at  the  angle  between  branches  there  are  distinct  lines  of 
rough  bark  that  have  been  pushed  up   and  broken   by   the   growth- 


*A  micron  is  about  one  twenty-five  thousandths  of  an  inch. 
fKryptogamen  Flora,  Die  Pilze  VI,  p.   520. 


[Bulletin  261]  melaxuma  of  the  walnut. 


141 


Fig.  2.  One  of  the  first  evidences  of  Melaxuma.  The  black  sappy  ooze  has 
appeared  at  the  outer  edges  of  the  killed  bark  at  the  crotch.  The  bark  between 
has  been  killed  and  pycnidia  of  Dothiorella  have  already  appeared  on  the  surface 
of  part  of  the  killed  bark. 


142 


UNIVERSITY   OF    CALIFORNIA EXPERIMENT    STATION. 


pressure  of  the  bases  of  the  two  adjoining  limbs.  These  places,  with 
their  extra  amount  of  functionless  bark  cells,  are  fertile  places  for  the 
germination  and  growth  of  the  fungus,  which  having  once  become 
thoroughly  established  as  a  saprophyte  appears  to  be  able  to  advance 
into  the  surrounding  live  bark.  Severe  winds  also  whip  the  branches 
about  and  probably  cause  slight  cracks  at  the  forks  of  the  branches. 


Fig.  3.  Melaxuma  cankers  as  they  occur  on  limbs  surrounding  the  base  of  dead 
twigs.  (A)  Old  canker  on  willow.  (B)  Old  caker  on  walnut.  (C)  Part  of  bark 
of  a  beginning  canker  on  walnut  cut  away  to  show  discolored  wood  underneath. 


Another  probable  entrance  for  the  fungus  is  in  unavoidable  injuries 
to  the  limbs  when  the  pickers  climb  the  trees  or  when  poles  are  used 
to  knock  off  the  nuts.  In  some  places  also  the  woodpeckers  line  the 
bark  with  rows  of  small  holes  (Fig.  5)  which  would  open  up  the  way 
for  the  entrance  of  the  fungus.     Then  it  would  seem  that  the  small 


[Bulletin  261]  melaxuma  of  the  walnut.  143 

twigs,  especially  on  the  inside  of  large  trees  that  are  possibly  weakened 
by  shading,  are  attacked  and  the  fungus  passes  easily  from  them  to  the 
larger  branches,  thus  forming  cankers.     (Fig.  3.) 

EXPERIMENTS  FOR  CONTROL. 

Having  proved  that  the  fungus  (Dothiorella  gregaria  Sacc.)  was  the 
cause  of  Melaxuma,  experiments  were  started  to  see  what  could  be  done 
in  controlling  the  disease.  Cankers  were  cut  out  so  as  to  remove  all  the 
diseased  bark,  as  well  as  the  black,  killed  wood  underneath,  and  the 
wounds  were  treated  with  strong  lime-sulphur  solution,  and  with 
Bordeaux  paste  (see  formula  at  end  of  bulletin),  the  same  that  had 
been  used  for  the  treatment  of  citrus  gummosis.  The  results  showed 
that  the  cankers  could  be  stopped  in  this  way  and  prevented  from 
enlarging  any  further.  Other  cankers,  not  treated,  enlarged  till  the 
limbs  were  killed. 

On  July  31,  1913,  the  following  experiments  were  tried  on  20-year 
old  trees : 

1.  A  canker  2  by  5  inches,  produced  by  inoculation  one  month  pre- 
viously with  a  bit  of  diseased  bark,  was  cut  out.  The  diseased  bark 
and  discolored  wood  was  cut  away,  leaving  a  wound  1  foot  long  and 
two-thirds  the  distance  around  the  limb.  The  wound  was  painted  with 
Bordeaux  paste. 

2.  An  infected  area  4  by  5  inches  just  started  on  side  of  trunk,  was 
cut  to  get  out  all  the  blackened  tissue  which  extended  only  one-half 
way  through  the  thick  bark.  The  area  was  then  painted  with  Bordeaux 
paste. 

3.  An  active  canker  on  a  3-inch  limb  was  cut  out  so  as  to  remove  all 
discolored  tissue,  making  a  wound  1  foot  long  and  one-half  way  around 
the  limb,  and  this  wound  was  treated  with  lime-sulphur  paste. 

4.  The  bark  on  a  canker  6  by  6  inches  on  the  side  of  a  trunk  was  cut 
away  and  all  discolored  wood  gouged  out  and  the  wound  painted  with 
Bordeaux  paste. 

5.  The  bark  on  a  large  old  canker  in  crotch  of  tree  was  cut  away 
well  into  the  live  part  on  one  edge  of  the  area,  but  not  on  the  other. 
Not  all  of  the  discolored  wood  was  cut  out.  The  wound  was  painted 
with  Bordeaux  paste. 

6.  The  same  kind  of  canker  in  another  tree  was  similarly  cut  and 
painted  with  lime-sulphur  paste. 

On  examination  of  these  experiments  on  April  29,  1914,  about  nine 
months  after  treatment  it  was  found  that  in  1,  2,  3,  and  4,  where  the 
cankers  had  been  carefully  cut  out,  the  disease  had  progressed  no 
further  and  the  cut  edges  were  all  healing ;  5  and  6  were  healing  on  the 
side  where  the  bark  was  cut  well  into  the  live  part,  but  were  progress- 
ing on  the  opposite  uncut  side  with  oozing  of  black  sap. 


144 


UNIVERSITY    OF    CALIFORNIA — EXPERIMENT    STATION, 


Fig.  4.  Two  inoculations  from  a  culture  of  Dothiorella  fungus  which  had  been 
isolated  from  a  Melaxuma  canker  of  walnut,  and  a  check.  Arrows  indicate  the 
location  of  the  cuts  made  through  the  bark.  Part  of  the  bark  cut  away  to  show 
the  discoloration  of  the  wood  in  the  cankers.  (A)  Canker  on  walnut  limb  four 
months  after  inoculation.  (B)  Canker  on  willow  limb  four  months  after  inocula- 
tion from  same  culture.  (C)  A  check  cut  in  another  willow  limb  into  which  no 
fungus  was  inserted,  showing  no  killing  of  tissue. 


[Bulletin  261]  melaxuma  of  the  walnut.  145 

In  April,  1914,  two  large  cankers  in  the  crotches  in  two  trees  were 
cut,  one  by  getting  out  all  discolored  wood  underneath,  and  the  other 
by  cutting  back  to  healthy  bark  but  leaving  the  discolored  wood.  Both 
of  these  later  healed  well  on  the  cut  edges  without  further  enlargement 
of  the  cankers. 

Further  experiments  were  begun  at  this  time  on  a  larger  scale, 
treating  entire  trees  by  cutting  out  cankers  and  dead  limbs  and  treating 
different  trees  with  Bordeaux  paste,  lime-sulphur  paste  and  asphalt 
paint.  Of  these,  the  Bordeaux  paste  appeared  to  give  the  best  average 
results. 

A  little  later,  control  work  on  a  larger  scale  was  carried  on  in 
co-operation  with  several  large  walnut  growers  in  Santa  Barbara 
County.  Mr.  C.  W.  Beers,  Horticultural  Commissioner  of  Santa 
Barbara  County,  has  given  much  assistance  in  this  work.  A  large 
grower  in  Santa  Barbara  County  started  cutting  out  these  cankers  and 
dead  limbs  on  a  rather  extensive  scale,  having  treated  more  than  100 
acres.  The  work  was  begun  in  August,  1914.  After  cutting  out  the 
cankers  the  areas  were  covered  with  Bordeaux  paste.  Other  growers 
have  not  only  cut  out  the  cankers  but  painted  the  entire  trunks  and 
crotches  of  the  trees  with  Bordeaux  paste  as  a  prevention  against 
further  infection. 

The  results  of  this  work  are  so  far  quite  promising.  All  except  a 
very  few  of  the  wounds  where  cankers  have  been  cut  out  are  healing 
perfectly  without  further  spread.  In  treating  these  trees  on  a  com- 
mercial scale,  the  blackened  wood  in  many  of  the  areas  was  not  entirely 
cut  out  because  of  the  expense,  and  yet  in  most  cases  these  also  seemed 
to  be  stopped  and  showed  no  activity  the  next  year.  In  one  orchard 
of  about  forty  acres,  the  work  was  more  hurried  at  the  last  than  at  the 
first,  the  cankers  and  dead  limbs  not  being  cut  out  so  thoroughly.  In 
the  part  of  the  orchard  treated  last,  the  results  are  not  nearly  so  good, 
and  a  considerable  number  of  cankers  are  still  showing  signs  of  activity. 
In  the  part  where  the  work  was  first  begun  and  executed  with  more 
care,  very  few  old  cankers  show  any  signs  of  enlarging. 

Experiments  in  spraying  with  lime-sulphur  and  Bordeaux  mixture 
in  conjunction  with  cutting  out  the  diseased  cankers  are  now  being 
carried  on.  There  has  not  been  sufficient  time  to  obtain  any  data  from 
this  later  work. 

TREATMENT   SUGGESTED. 

From  the  observations  and  results  of  experiments  so  far  made,  the 
following  tentative  treatment  is  suggested: 

1.  Cut  out  the  cankers  that  have  not  gone  too  far  on  the  trunk  and 
larger  limbs  and  disinfect  the  wounds  thus  made.  (Fig.  5.)  The 
dead  and  discolored  bark  should  be  cut  away,  getting  a  little  beyond  the 


146 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION. 


margin  of  dead  tissue.  If  the  cankers  are  not  large  and  the  wood  under- 
neath has  not  been  stained  deeply,  it  will  pay  to  dissect  out  all  the 
discolored  wood  as  well  as  the  bark.  Probably  one  of  the  best  disin- 
fectants to  apply  to  the  wound  is  the  Bordeaux  paste,  the  same  that  is 


Fig.  5.  Walnut  trees  showing  the  location  of  Melaxuma  cankers  that  had  been 
cut  out  and  treated  with  Bordeaux  paste  the  year  previous.  Notice  the  rows  of 
holes  in  the  bark  of  one  tree,  made  by  woodpeckers.  These  probably  served  in 
this  case  as  partial  means  of  infection. 


recommended  for  lemon  gummosis.  If  the  canker  is  large  and  has  been 
in  the  tree  a  long  time,  the  wood  may  be  stained  so  deep  as  to  render  the 
work  of  cutting  out  all  discolored  wood  too  expensive.  If  the  canker  has 
practically  girdled  the  limb  (as  at  X  in  Fig.  1,  B),  the  limb  had  better 


[Bulletin  261]  melaxuma  of  the  walnut.  147 

be  cut  out.  The  limb  at  Y,  Fig.  1,  B,  can  probably  be  saved  for  a 
number  of  years  by  cutting  back  into  the  healthy  bark  around  the  edge 
of  the  killed  area,  either  with  or  without  cutting  out  the  discolored 
wood,  and  disinfecting  it.  It  would  be  safer,  however,  if  expense  in  time 
is  not  too  great,  to  also  dissect  out  the  stained  wood,  especially  if  this 
has  begun  to  soften  and  decay.  Trees  need  not  get  to  the  condition  of 
Fig.  1,  A  and  B,  if  they  are  watched  from  year  to  year.  They  may  be 
treated  when  the  areas  are  starting  as  in  Figs.  2  and  3.  Some  weeks  or 
months  later  after  it  is  seen  that  the  progress  of  the  cankers  is  stopped 
and  the  bark  is  healing  at  the  cut  edges  as  in  Fig.  5,  the  exposed  wood 
should  be  covered  with  asphalt  paint.  If  the  Bordeaux  paste  has  not 
been  washed  away  by  that  time  or  has  not  largely  peeled  off  from  the 
wood,  the  excess  may  be  removed  with  a  wire  brush  before  applying  the 
paint. 

2.  The  limbs  with  cankers  too  large  to  be  treated,  as  well  as  the  limbs 
already  dead,  should  be  pruned  out  with  a  saw  or  pruning  shears,  making 
smooth  cuts  and  leaving  no  stubs.  An  ax  should  not  be  used  in  pruning. 
The  larger  cuts,  one  inch  or  larger,  may  be  disinfected  with  corrosive 
sublimate,  1-1000  parts  of  water,  and  painted  with  asphalt  paint  or 
other  good  covering.  The  Bordeaux  paste  is  apparently  not  so  good  to 
use  on  the  cuts  made  in  pruning  out  limbs. 

3.  As  an  added  preventive  against  the  development  of  new  cankers 
in  the  future,  the  entire  trunks  and  the  crotches  of  all  trees  in  the 
orchard  (both  affected  and  non-affected)  may  be  painted  with  Bordeaux 
paste  at  small  expense  per  tree.  It  must  be  borne  in  mind  in  this  con- 
nection that  some  new  cankers  will  undoubtedly  make  their  appearance 
after  painting  with  Bordeaux  paste.  They  will  have  started  unnoticed, 
the  fungus  having  already  gotten  into  or  through  the  bark  before  the 
Bordeaux  paste  was  applied,  as  in  Fig.  2.  After  a  year  or  two  when  all 
these  have  been  worked  out,  the  application  of  Bordeaux  paste  ought  to 
prevent  new  ones  from  forming,  except  where  severe  injuries  have  been 
made. 

4.  All  injuries  to  the  bark  in  cultivating  the  orchards  should  be 
avoided.  The  injury  inflicted  on  the  trunks  of  walnut  trees  in  some 
orchards  in  plowing  and  cultivating  is  inexcusable.  It  is  a  common  sight 
in  some  orchards  to  see  every  third  or  fourth  tree  trunk  with  a  large 
patch  of  bark  torn  or  wounded  by  parts  of  the  harness  or  the  edge  of 
the  plow,  and  to  see  the  lower  limbs  with  bark  torn  off  by  the  harness 
of  the  passing  team.  All  these  injuries  are  ideal  places  for  the 
Melaxuma  fungus  to  enter  and  start  a  canker. 

5.  If  willows  are  growing  along  the  edges  of  a  walnut  orchard,  it 
would  be  well  to  destroy  them  or,  in  case  they  are  useful  in  keeping  the 
soil  from  washing,  to  keep  them  cut  back  every  year  or  two.     The  young 


148  UNIVERSITY   OP    CALIFORNIA EXPERIMENT    STATION. 

healthy  shoots  do  not  seem  to  be  as  subject  to  the  disease  as  older, 
larger  limbs. 

Bordeaux  Paste.  The  formula  for  Bordeaux  paste  is  as  follows  :  12  pounds  of 
Milestone  (copper  sulphate)  dissolved  in  8  gallons  of  water  in  a  wooden,  earthen 
or  glass  vessel ;  and  24  pounds  of  quick-lime  slaked  in  8  gallons  of  water.  When 
the  lime  is  cool,  stir  together  about  equal  parts  by  volume  of  each  for  making 
enough  mixture  to  last  for  one  day  only.  The  Milestone  is  easiest  dissolved  by 
suspending  it  in  a  sack  at  the  top  of  the  water  over  night.  If  the  Milestone  's 
pulverized  and  suspended  in  warm  water  it  dissolves  rapidly.  Good  lime  that  is 
not  air-slaked  should  be  used,  and  after  slaking  it  with  the  water  it  should  be 
allowed  to  cool  before  being  used  in  making  paste.  If  covered  to  avoid  evaporation 
each  ingredient  will  keep  indefinitely,  but  after  mixing,  the  paste  slowly  deteriorates. 
Where  it  is  being  used  over  a  number  of  days  or  weeks,  just  enough  of  the  wet 
slaked  lime  and  the  bluestone  solution  should  be  mixed  to  make  paste  enough  to 
last  for  one  day,  leaving  the  remainder  unmixed  in  separate  vessels.  It  may  be 
applied  with  large  brushes,  as  is  whitewash. 

Asphalt  Paint.  Good  asphalt  paint  free  from  impurities  may  be  made  by 
dissolving  hard  asphalt  in  benzine  or  gasoline  until  it  has  body  enough  to  form  a 
good  covering  when  applied  with  the  brush.  The  hard  asphalt  may  either  be 
broken  into  small  pieces  and  dissolved  in  the  benzine,  or  the  asphalt  may  first 
be  melted  by  heating,  and  after  it  has  been  taken  from  the  fire  and  cooled  down 
somewhat,  but  not  enough  to  harden  again,  the  benzine  poured  in  and  stirred. 

Asphalt  paint  dissolved  in  benzine  and  put  up  in  cans  ready  for  use,  can  usually 
be  purchased  at  paint  shops  or  hardware  stores.  A  similar  article  dissolved  in 
turpentine  is  also  on  the  market,  but  is  not  suitable  for  use  on  tree  wounds. 

SUMMARY. 

1.  Melaxuma,  a  walnut  disease  in  California,  occurring  as  black 
cankers  on  the  trunk,  crotches,  and  large  limbs,  and  also  occasionally 
as  a  withering  of  small  branches,  has  attracted  serious  attention  in  Santa 
Barbara  and  Ventura  counties  in  the  last  two  or  three  years. 

2.  Experiments  have  shown  that  the  Melaxuma  cankers,  as  well  as  the 
wilting  of  the  branches,  are  caused  by  the  entrance  of  a  fungus  which 
has  been  identified  as  Dothiorella  gregaria. 

3.  This  fungus  was  found  in  the  diseased  portion  of  Melaxuma 
cankers,  was  isolated  in  pure  cultures,  inserted  in  cuts  in  healthy  limbs, 
and  was  found  to  produce  typical  Melaxuma  cankers  on  large  limbs 
and  the  wilting  of  small  branches.  The  fungus  was  then  reisolated 
from  these  artificially  produced  cankers  and  found  to  be  the  same  as 
that  inserted. 

4.  The  same  species  of  fungus  was  discovered  on  the  arroyo  willow, 
Salix  lasiolepis,  in  Santa  Barbara  County,  from  which  it  probably 
spread  to  the  walnut  trees. 

5.  Experiments  and  observations  would  indicate  that  the  disease  may 

be  successfully  checked  by  the  following  methods,  the  details  of  which 

are  given  on  preceding  pages :  By  cutting  out  the  cankers  and  the  dead 

and  weakened  limbs  and  disinfecting  the  cuts ;  by  painting  the  crotches 

and  trunks  of  all  trees  with  Bordeaux  paste  or  other  fungicides ;  by 

avoiding  injuries  to  the  bark;  and  by  keeping  willows  near  walnut 

orchards  cut  back. 

o 


